Given sample A and sample B of DNA, can a it be determined with a scientific certainty that, say, sample A is human and sample B is simian?
Yep.
Thanks, Dex. A follow-up, please. Is the DNA of a fetus the same as the DNA of its mother?
The fetus derives 1/2 of its DNA from its Mother and 1/2 from its Father.
Half of the nuclear DNA is. The other half is from the father. All of the mitochondrial DNA is from the mother.
Bear in mind that much of the DNA of both parents - more than 99% - is identical anyway.
Nope.
The DNA of a fetus is a combination of the DNA of its mother and father. This is why paternity tests work.
The only humans that have identical DNA are identical twins, and clones. So, in theory -if you were a twin (or a clone) you could be convicted/acquitted on the basis of your twin’s (clone’s) DNA.
The DNA of animals is sufficiently different from human DNA that you could not be convicted/acquitted on the basis of your dog’s DNA. 
Does that help?
What could both you AND your dog be charged with? Littering?
Is this leading to an abortion discussion?
:eek:
I remember reading somewhere that over 90 per cent of human DNA is the same as that of the chimps (our closest relative among the primates). I can’t remember, 96%, 98%? Whatever the difference is, it’s enough to dedect, however.
The trouble with the abortion angle is that it is not clear that every entity with human DNA is a person. A hair sample or a liver biopsy sample has human DNA, but is not a person.
There is the famous example of HeLa cells. These were human cells taken from a cancerous tumor and used for research purposes. The cells were so agressive that they are sometimes found invading and contaminating other tissue cultures. In effect they are protozoans with 100% human DNA.
See:
http://www.madsci.org/posts/archives/may97/860431113.Cb.r.html
We share more than 90% of our DNA with chimpanzees, but I, too, don’t recall the exact figure.
We share significant portions of our DNA with nearly all animals, anyway. It’s the wonders of evolution and the fact we have never had a reason to make a serious change. In fact, our basic bodyplan (long torso with digestive tract running right down the center) was first evolved by … you guessed it … worms. Remove the appendages and a human will still live, something we inherited from our wormy ancestry. 
Looking at this link http://www.answersingenesis.org/docs2002/1125dna.asp
I don’t think typical DNA tests would be able to differentiate the two. It would take a karyotype of the entire genome to detect the differences. Remember that DNA testing uses the “nonsense” areas of the chromosome and that it can determine if the DNA came from a single source it tells nothing about what that source is.
Did you really post a link to ANSWERS IN GENESIS?!?!?!?
Do you know what the word “karyotype” means?
This message board is supposed to fight ignorance, not perpetuate it.
Why not?
I don’t think you know what “karyotype” means.
What do you mean, exactly, by “DNA testing”?
Ack, I didn’t realize where I was and just glanced at what it said. The facts concerning similarity of genotypes is accurate (greater than 95%) , and I had no idea that it was an anti-evolution site. Shows what happens when you try to play at work.
Yes, I know what a karyotype is and said genome, but meant comparing the appearance of all the chromosomes in an intact nucleus.
By DNA testing I meant what is currently used in the legal system, either PCR or RFLP. Both tests give no information as to what species the sample came from.
Does biology define the term “person” or “human being”? Or must that be defined by a branch of philosophy other than science? Say, ethics, maybe?
OK, that’s better. Given the nature of the link, I wanted to know where you were coming from. 
I agree with you, the info you linked to is surprisingly correct considering that it’s posted on a creationist site. The point that the percentage of similarity between chimps and humans varies with what kind of differences are considered is perfectly valid.
They don’t give species information in and of themselves. However, they can be used to identify species when used in conjunction with a data bank. Here is an example of using PCR to determine the species of a sample of tuna.
The latter.
Biologists may try to define, in scientific terms, what is meant by an “individual,” a “species,” a "member of the species Homo sapiens, etc., but even these definitions may be open to dispute. I do not think that “person” or “human being” are, by their nature, scientific terms.
You can define “human being” scientifically, by saying that any member of the species Homo sapiens is a human being. And we can use the biological species concept. But that is not satisfactory ethically, since it would mean that people who can’t interbreed would not be human!
In my opinion, “Personhood” is a legal and/or ethical concept, not a scientific concept. Science can give you information on which you can base your ethical judgements.
For instance, we could ethical judge dolphins and elephants and intelligent robots to be “people”, even if they aren’t humans. And going the other way, we don’t judge human tissue to be a person neccesarily.
I’m pretty comfortable in not having a rigorous definition of personhood, since I doubt human competence in making that definition. There will always be cases that no one considered when making the rules. Although all persons must have some sort of brain activity, I still don’t want anencephalic babies to be judged things.
The bottom line is that biology can reveal that there is no sharp demarcation in these categories. A single cell taken from your finger is not a human being. But is a single fertillized egg cell? What exactly is the difference? Is there a difference if we take the nucleus from your finger cell and insert it in a fertillized egg cell? Are identical twins one person or two? How about conjoined twins that share a body but have two heads? Would it make a difference if one of the twins had brain damage and was in a permanent vegetative state and the other wasn’t? What about conjoined twins with two bodies but one head? How about a person with an extra leg?
For the vast majority of human beings there isn’t any confusion between where the individual starts and stops. But for many other species this isn’t the case. Take grass…grass usually reproduces by new blades springing up from underground rhizomes. This means that the new blades are genetically identical to the parent blade. But are they new individual grass organisms, or is the individual organism the patch of grass that includes many blades, like a tree contains many leaves? Does it make a difference if you take a hoe and cut the patch in two?
Anyway, the point of all this rambling is to demonstrate that personhood and individuality are ethical decisions informed by science, not scientific decisions.
While we have the various DNA test experts assembled, allow me to slightly hijack thusly:
Could the common PCR or RFLP tests distinguish me from my non-twin brother? My sister? My half-brother or -sister, either with the same mother or father?
The specific situation which occurrs in the screenplay I’m writing is that a man attempts to fake his own death by substituting the burned-beyond-recognition body of his brother and assuming his identity. Would a DNA test be able to tell the difference?